Field of the Invention
The present invention relates to a technique for processing a substrate with a film having a porous structure (porous film) formed on a surface layer thereof. Examples of the substrate to be processed include e.g., a semiconductor wafer, a substrate for a liquid crystal display device, a substrate for a plasma display, a substrate for an FED (Field Emission Display), a substrate for an optical disk, a substrate for a magnetic disk, a substrate for a magneto-optical disk, a substrate for a photomask, a ceramic substrate, and a substrate for a solar battery.
Description of the Background Art
In a manufacturing process of a semiconductor device and a liquid crystal display device, a cleaning process for removing foreign substances from a substrate, such as a semiconductor wafer and a glass substrate for a liquid crystal display device, is carried out. For the cleaning process, for example, Japanese Patent Application Laid-Open Nos. 2009-21617 and 2011-77153 disclose a technique in which a so-called two-fluid nozzle is used to mix deionized water with gas for generating droplets of the deionized water, and the droplets of the deionized water is injected to a substrate to physically remove foreign substances adhering to the substrate by the kinetic energy of the droplets of the deionized water which are collided with the substrate.
In recent years, to meet a request to lower the dielectric constant of an interlayer dielectric film, a technique in which a film having a relative permittivity of 2.5 or less (a so-called Ultra Low-k film: ULK film), which has difficulty in being achieved with a dense film, is achieved with a porous film having a porous structure has been in practical use.
As described in US 2003/178047, such a porous film resists water (water causes change in dielectric constant), and consequently, it is unfavorable that the porous film is cleaned with the deionized water. Accordingly, for example, US 2003/178047 proposes that in place of the deionized water, IPA (isopropyl alcohol) is used to clean the substrate having the porous film.
When the droplet generation conditions (the flow rate of a processing solution and the flow rate of the gas) are made equal to compare the case of using the IPA as the processing solution to clean the substrate with droplets of the IPA with the case of using the deionized water as the processing solution to clean the substrate with droplets of the deionized water, it is found that the former can obtain only a lower foreign substance removal effect than the latter. Therefore, when the substrate with the porous film formed on the surface layer thereof is cleaned only with the droplets of the IPA, not with the deionized water, although damages to the substrate are prevented, no foreign substances can be removed sufficiently from the substrate unless injection of the droplets of the IPA is continued for a considerably long time. In this form, the processing time becomes long, and the IPA consumption amount cannot be avoided from increasing. Consequently, an alternative method which can sufficiently clean the substrate with the porous film formed on the surface layer thereof has been demanded.